1. Field of the Invention
The invention relates to induction heating, and in particular to a coreless induction furnace or induction heated channel furnace and a lining material therefor.
2. Description of the Prior Art
A coreless induction furnace usually comprises a vessel having a refractory crucible inside a water cooled induction coil. The innerface of the induction coil is usually covered by a thin layer of refractory plaster which is called the coil grout. There is a need to interpose a layer between the coil grout and the refractory crucible to provide a slip plane between these two surfaces. FR-A-2101903 discloses an induction furnace having a slip plane comprising a layer of spun glass fiber.
According to the invention in one aspect there is provided an induction furnace comprising a vessel comprising a refractory crucible within a cooled induction coil, slip plane material and supporting material being present between the crucible and the coil, characterized in that the slip plane material comprises a flexible mica paper or sheet.
In a much preferred feature the slip plane material and the supporting material are present as a laminate.
Preferably the supporting material therefor is a glass fiber fabric. Preferably the glass fabric has a density of between about 500 g/m2 and about 1500 g/m2, preferably 800 to 1350 g/m2 and a thickness of between 0.8 to about 2.5 mm. preferably 1.4 mm. to 2.2 mm. Preferably the glass fiber fabric is woven.
In another aspect the invention provides a method of preparing a coreless induction furnace comprising a vessel having a refractory crucible surrounded by a cooled induction coil, the method comprising locating a slip plane material L1 and other material (L2) in between, characterized by interposing a layer of flexible mica or sheet as the slip plane material (L1) between the refractory crucible wall (2) and the surrounding cooled inducting coil.
In yet another aspect the invention provides for use in the lining of an induction furnace as defined, a laminate comprising a layer of flexible mica paper or sheet and supporting layer of glass fiber fabric. The two layers being held together by an inorganic binder.